1. Field of the Invention
The present invention relates to apparatus and method for performing cavitation peening, and, more particularly, the present invention relates to sealing a cavitation zone in which to perform cavitation peening.
2. Description of the Related Art
Peening is a process of introducing mechanical stress into the surface layer of a part to compress and strengthen it against future fractures and wear. Peening can be performed in a variety of manners, including shot peening, laser peening and cavitation peening. Cavitation peening involves the application of bubbles onto the surface with the part in a liquid environment. The collapsing of the bubbles imparts impactive forces to the part. One difficulty with prior cavitation peening apparatus and methods is that the entire part to be treated is placed in the liquid environment. This can be difficult to achieve, especially when the part to be treated is itself large or is a part of a large apparatus or system.
While the present invention may be used in a variety of industries, the environment of a nuclear power plant will be discussed herein for illustrative purposes. A nuclear power plant has a nuclear reactor housed within a pressure vessel and a reactor coolant system (RCS) for removing heat from the reactor and to generate power. Nozzles are attached to the vessels and/or piping for a number of purposes, such as for connecting piping and instrumentation, providing vents, and securing control element drive mechanisms and heater elements.
The nuclear industry is required to perform inspections of such nozzles, as well as their welds, due to the emergence of primary water stress corrosion cracking (PWSCC). Stress corrosion cracking occurs in a material due to a combination of a corrosive environment and tensile forces placed on the material. Cracking can be induced in materials in different ways including cold forming, welding, grinding, machining, and heat treatment as well as other physical stresses placed on the material. Stress corrosion cracking in nuclear reactor environments is a significant phenomenon that must be carefully monitored for successful operation of a nuclear power plant facility. Without careful monitoring for PWSCC, material defects may begin and may ultimately damage the material. If cracking continues, the materials may be damaged to such an extent that the materials must be removed from service and replaced. In the nuclear reactor environment, such replacement of components is extremely undesirable due to radiological concerns related to worker and facility safety, as well as overall plant economic concerns.
Thus, what is needed is an apparatus and method of mitigating or preventing the initiation of stress corrosion cracking.